php 8.4 deprecations

These can be cleaned up easily with rector, but I don't know if they'd cause a BC break.

Deprecated: cebe\openapi\SpecBaseObject::resolveReferences(): Implicitly marking parameter $context as nullable is deprecated, the explicit nullable type must be used instead in /home/tac/sites/packages/vendor/cebe/php-openapi/src/SpecBaseObject.php on line 396

Deprecated: cebe\openapi\SpecObjectInterface::resolveReferences(): Implicitly marking parameter $context as nullable is deprecated, the explicit nullable type must be used instead in /home/tac/sites/packages/vendor/cebe/php-openapi/src/SpecObjectInterface.php on line 43

Deprecated: cebe\openapi\spec\Paths::resolveReferences(): Implicitly marking parameter $context as nullable is deprecated, the explicit nullable type must be used instead in /home/tac/sites/packages/vendor/cebe/php-openapi/src/spec/Paths.php on line 249

Deprecated: cebe\openapi\spec\PathItem::resolveReferences(): Implicitly marking parameter $context as nullable is deprecated, the explicit nullable type must be used instead in /home/tac/sites/packages/vendor/cebe/php-openapi/src/spec/PathItem.php on line 153

Deprecated: cebe\openapi\spec\Responses::resolveReferences(): Implicitly marking parameter $context as nullable is deprecated, the explicit nullable type must be used instead in /home/tac/sites/packages/vendor/cebe/php-openapi/src/spec/Responses.php on line 239

Deprecated: cebe\openapi\spec\Reference::__construct(): Implicitly marking parameter $to as nullable is deprecated, the explicit nullable type must be used instead in /home/tac/sites/packages/vendor/cebe/php-openapi/src/spec/Reference.php on line 72

Deprecated: cebe\openapi\spec\Reference::resolve(): Implicitly marking parameter $context as nullable is deprecated, the explicit nullable type must be used instead in /home/tac/sites/packages/vendor/cebe/php-openapi/src/spec/Reference.php on line 179

Deprecated: cebe\openapi\spec\Reference::resolveReferences(): Implicitly marking parameter $context as nullable is deprecated, the explicit nullable type must be used instead in /home/tac/sites/packages/vendor/cebe/php-openapi/src/spec/Reference.php on line 366

Überprüfe die Signaturen von resolveReferences und den Konstruktoren in src/SpecBaseObject.php, src/SpecObjectInterface.php sowie in src/spec/Paths.php, PathItem.php, Responses.php und Reference.php. Prüfe das Deprecation-Verhalten von PHP 8.4 und ob die Signaturänderungen die Kompatibilität erhalten; abgeschlossen ist die Aufgabe, wenn die gemeldeten Deprecations ohne einen BC-Break behoben sind.

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